Rapid yet Controlled Synthesis of 2D Covalent Organic Framework Nanocapsules as High-Performance Photocatalytic Carriers

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Summary:
The authors from Zhejiang University developed a 2D covalent organic framework (COF) nanocapsule with high crystallinity and hierarchical pores, achieving high efficiency in photocatalytic hydrogen production.

Background:
1. The synthesis of 2D polymers such as COFs often faces a trade-off between high reaction rates and precise morphology control. Previous methods, including solvothermal and microwave-assisted synthesis, are either time-consuming or result in poor crystallinity and irregular structures.
2. The authors proposed a rapid yet controlled synthesis strategy using oil-in-water (O/W) emulsion droplets stabilized by cationic surfactants, achieving high reaction rates and well-defined nanostructures.

Research Content:
1. Synthesis:
1) Imine based two-dimensional covalent organic frameworks TAPB-BTCA-COF, TFPA-TAPB-COF and TFPB-TAPB COFs were synthesized by using the water in oil (O/W) lotion drop interface nano confinement method (for related products, please click the link).
2) Using cetyltrimethylammonium bromide (CTAB) as emulsifier, the acetate containing 1,3,5-tris (4-aminophenyl) benzene (TAPB) was mixed with water phase and then ultrasonic treated to prepare lotion.
3) The acetate solution containing 1,3,5-benzenetrialdehyde (BTCA) is added to the lotion drop by drop through the metering pump to ensure that the polymerization reaction takes place at the interface.
4) Within 4.5 hours at room temperature, a yield of up to 86% can be achieved without the need for additional catalysts.
2. Characterizations:
   1) BET specific surface area reached up to 139.0 m²/g, with micropores at 1.4 nm and mesopores at ~5.0 nm.
   2) SEM/TEM tests showed uniform spherical particles with diameters of 114–565 nm and shell thicknesses of 12–63 nm.
   3) XPS and UV-Vis spectroscopy confirmed the COF structure and energy band suitable for hydrogen evolution.
3. Application:
   The COF nanocapsules demonstrated high efficiency in photocatalytic hydrogen production, reaching a stable rate of 10.2 mmol·g⁻¹·h⁻¹ for 6 hours.
4. Mechanism:
   The surfactant acted as a catalyst and regulated pore formation. The microdroplet interface accelerated the reaction by two orders of magnitude compared to bulk reactions. The hollow structure and hierarchical pores enhanced photocatalytic performance.

Outlook:
This research provides a rapid and controlled synthesis method for 2D COF nanocapsules with high efficiency in photocatalytic applications, promoting the development of advanced 2D polymeric materials.

Rapid yet Controlled Synthesis of 2D Covalent Organic Framework Nanocapsules as High-Performance Photocatalytic Carriers
Authors: Yuting Ma, Shenhui Yu, Wei Li, Di Chen, Zhenqian Zheng, Linjie Mao, Xuan Yang, Wen-Jun Wang, Pingwei Liu
DOI: 10.1002/anie.202416980
Link: https://onlinelibrary.wiley.com/doi/10.1002/anie.202416980

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